(4) Lock detect threshold voltage

The LB1660 series have the function to stop the output drive after the lapse of a given period of time when a motor is

locked, and period of time can be set by C, R3.

The CR pin peripheral equivalent circuit is shown below. The LB1660 series generate the CR pin discharge pulse when the

phase changes, (detection of rotation). When a motor is locked (very low rotational speed), the C connected to the CR pin

output drive current becomes zero and the output transistor is turned off, and the RD pin output turns from ‘‘L’’ to ‘‘H’’. The

RD pin output is of the open collector type.

CR Pin Peripheral Circuit

[Setting Method of Lock Detect Time]

(1) Generation of discharge pulse

Electric charges on C charged through R3 are discharged via route of C

→ r → TRr with constant width pulses at each phase

The discharge pulses are generated by two methods as shown below.

1 Generated internally at the time of phase change. The power transistor base storage time is used for discharge pulses.

t = 15 to 30 µsec

2 When the kickback voltage induced by L of a motor coil is absorbed by the zener diode across collector and base of the

output transistor, this interval of time during which the transistor is turned on is used for discharge pulses.

Therefore, the LB1661,1665 or LB1660N, 1664N use external zener diodes and capacitors, discharge occurs with pulses

is the same.

Output transistor drive

Discharge pulse

CR pin voltage

RD pin

Motor lock

Output off

LB1660N, 1661, 1664N, 1665

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